Hi Laurent,

On Tue, Jun 21, 2011 at 17:36, Laurent Pinchart
[off-list ref] wrote:

+The following types and visuals are supported.
+
+- FB_TYPE_PACKED_PIXELS
+
+- FB_TYPE_PLANES

You forgot FB_TYPE_INTERLEAVED_PLANES, FB_TYPE_TEXT, and
FB_TYPE_VGA_PLANES. Ah, that's the "feel free to extend the API doc"  :-)

+The FOURCC-based API replaces format descriptions by four character codes
+(FOURCC). FOURCCs are abstract identifiers that uniquely define a format
+without explicitly describing it. This is the only API that supports YUV
+formats. Drivers are also encouraged to implement the FOURCC-based API for RGB
+and grayscale formats.
+
+Drivers that support the FOURCC-based API report this capability by setting
+the FB_CAP_FOURCC bit in the fb_fix_screeninfo capabilities field.
+
+FOURCC definitions are located in the linux/videodev2.h header. However, and
+despite starting with the V4L2_PIX_FMT_prefix, they are not restricted to V4L2
+and don't require usage of the V4L2 subsystem. FOURCC documentation is
+available in Documentation/DocBook/v4l/pixfmt.xml.
+
+To select a format, applications set the FB_VMODE_FOURCC bit in the
+fb_var_screeninfo vmode field, and set the fourcc field to the desired FOURCC.
+The bits_per_pixel, red, green, blue, transp and nonstd fields must be set to
+0 by applications and ignored by drivers. Note that the grayscale and fourcc
+fields share the same memory location. Application must thus not set the
+grayscale field to 0.

These are the only parts I don't like: (ab)using the vmode field (this
isn't really a
vmode flag), and the union of grayscale and fourcc (avoid unions where
possible).

What about storing the FOURCC value in nonstd instead?
As FOURCC values are always 4 ASCII characters (hence all 4 bytes must
be non-zero),
I don't think there are any conflicts with existing values of nonstd.
To make it even safer and easier to parse, you could set bit 31 of
nonstd as a FOURCC
indicator.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds